1. Field of the Invention
The present invention relates to an SOI (silicon on insulator) substrate. In addition, the present invention relates to a semiconductor device manufactured using the SOI substrate.
Note that a semiconductor device in this specification refers to all devices that can function by utilizing semiconductor characteristics. For example, electro-optic devices, semiconductor circuits, and electronic devices all fall into the category of a semiconductor device.
2. Description of the Related Art
An integrated circuit that uses a semiconductor substrate called an SOI substrate, which is provided with a thin single-crystalline semiconductor layer on an insulating surface, has been developed, replacing a silicon wafer formed by cutting an ingot of a single-crystalline semiconductor into thin slices. Using an SOI substrate can reduce parasitic capacitance between a drain of a transistor and a substrate. Therefore, the SOI substrate has been drawing attention as a means of improving the performance of a semiconductor integrated circuit.
Among methods of manufacturing SOI substrates, there is known a hydrogen ion delamination method (also called a Smart Cut® method in some cases) (for example, see Reference 1: U.S. Pat. No. 6,372,609). The method of forming an SOI in Reference 1 includes the steps of implanting hydrogen ions into a silicon wafer to form a fine bubble layer at a position of a predetermined depth from the surface, and then bonding the hydrogen-ion-implanted silicon wafer to another silicon wafer with a silicon oxide film interposed therebetween. After that, heat treatment is applied to delaminate the hydrogen-ion-implanted wafer in a thin-film form, with the fine bubble layer used as a cleavage plane. The hydrogen ion delamination method is also called a Smart Cut® method in some cases.
However, a damage layer produced due to the hydrogen ion implantation remains on the surface of the SOI wafer after the delamination. In Reference 1, a method of removing the damage layer is disclosed. In Reference 1, after the delamination step, an oxide film is formed on the surface of the SOI substrate by heat treatment in an oxidizing atmosphere. Then, the oxide film is removed and heat treatment of 1000 to 1300° C. is applied in a reducing atmosphere.
Also, there is known an SOI substrate which is obtained by bonding a silicon layer separated from a silicon wafer to a glass substrate (for example, see Reference 2: Japanese Published Patent Application No. 2004-087606 and Reference 3: Japanese Published Patent Application No. H11-163363).